Faroe Shetland Research Articles

Basin structure and prospectivity of the NE Atlantic volcanic rifted margin: cross-border examples from the Faroe–Shetland, Møre and Southern Vøring Basins

Interpreted horizons within the Atlantic Margins (AM) area and borehole synthetic seismogram for the Tulipan 6302/6-1 borehole compared to the AMS fast track processed seismic data.

Exploration challenges along the North Atlantic volcanic margins: the intra-volcanic sandstone play in subsurface and outcrop

Abstract The margins of the North Atlantic rift are covered by an extensive succession of volcanic rocks, with up to 5 km of continental flood basalts, hyaloclastites and interbedded sedimentary rocks. The volcanic succession deteriorates seismic imaging and has hampered petroleum exploration in these areas. Focused research and pioneering exploration activity, however, has improved the understanding and development of new play models in volcanic-influenced basins. In 2004, the Rosebank discovery finally proved that intra-volcanic siliciclastic sandstones of the Flett Formation may form attractive hydrocarbon reservoirs in the Faroe–Shetland Basin. The Kangerlussuaq Basin in southern East Greenland offers a unique opportunity to study the interaction of siliciclastic sediments with lavas and various volcaniclastic units. It is demonstrated that: (1) laterally extensive siliciclastic sedimentary units are present in the lower part of the volcanic succession; (2) the morphology of the lavas controlled variations in sandstone geometry and thickness; and (3) deposition of the interbedded sediments and lavas occurred in a low-relief environment close to sea level. The mineralogical composition of the intra-volcanic sediments is highly variable, ranging from siliciclastic to purely volcaniclastic. Diagenetic studies suggest that the nature of the volcanic component in volcaniclastic sandstones is more important to reservoir properties than the relative concentration.

Climatic Variability of the North Atlantic Oscillation Index and the Associated Fluctuations of Temperature and Water Mass Transport in the Upper Layer of the North Atlantic

Processes of formation of the North Atlantic Oscillation index (NAO) during different phases of the current (1868–2010) quasi-centurial variability of solar activity (the Wolf number) are considered. It is found that during the lowest solar activity of a quasi-centurial cycle, the NAO index tends to the value higher than those observed during maximum of solar activity. During the even cycles the NAO index tends to be a few times higher than those during the odd ones. The conceptual scheme is proposed assuming that at anomalously high NAO taking place mainly during even cycles, the western disturbance in the troposphere over the North Atlantic groves that intensifi es circulation in the upper layer of the subtropical gyre, leading to decrease of the amount of the Atlantic water mass infl owing to high latitudes. At anomalously low NAO observed mainly during the odd cycles, circulation in the subtropical gyre weakens that results in increase of the amount of the Atlantic water mass infl owing to high latitudes through the Faeroe–Shetland channel to the Norwegian and Barents seas. The range of the NAO variability is found (±0.5), at which average multi-year (climatic) regime of hydrometeorological characteristics is realized in the North Atlantic. Validity of the proposed conceptual scheme is confi rmed by the materials on water mass transport through the Faeroe–Shetland channel, formation of temperature anomalies in the North Atlantic upper layer and the Barents sea ice cover at NAO = ±0.5; NAO ≥ 1 and NAO ≤ –1.

An ocean–ice coupled response during the last glacial: a view from a marine isotopic stage 3 record south of the Faeroe Shetland Gateway

Abstract. The rapid climatic variability characterising the Marine Isotopic Stage (MIS) 3 (~60–30 cal ka BP) provides key issues to understand the atmosphere–ocean–cryosphere dynamics. Here we investigate the response of sea-surface paleoenvironments to the MIS3 climatic variability through the study of a high resolution oceanic sedimentological archive (core MD99-2281, 60°21' N; 09°27' W; 1197 m water depth), retrieved during the MD114-IMAGES (International Marine Global Change Study) cruise from the southern part of the Faeroe Bank. This sector was under the proximal influence of European ice sheets (Fennoscandian Ice Sheet to the East, British Irish Ice Sheet to the South) during the last glacial and thus probably responded to the MIS3 pulsed climatic changes. We conducted a multi-proxy analysis of core MD99-2281, including magnetic properties, x-ray fluorescence measurements, characterisation of the coarse (>150 μm) lithic fraction (grain concentration) and the analysis of selected biogenic proxies (assemblages and stable isotope ratio of calcareous planktonic foraminifera, dinoflagellate cyst – e.g. dinocyst – assemblages). Results presented here are focussed on the dinocyst response, this proxy providing the reconstruction of past sea-surface hydrological conditions, qualitatively as well as quantitatively (e.g. transfer function sensu lato). Our study documents a very coherent and sensitive oceanic response to the MIS3 rapid climatic variability: strong fluctuations, matching those of stadial/interstadial climatic oscillations as depicted by Greenland ice cores, are recorded in the MD99-2281 archive. Proxies of terrigeneous and detritical material suggest increases in continental advection during Greenland Stadials (including Heinrich events), the latter corresponding also to southward migrations of polar waters. At the opposite, milder sea-surface conditions seem to develop during Greenland Interstadials. After 30 ka, reconstructed paleohydrological conditions evidence strong shifts in SST: this increasing variability seems consistent with the hypothesised coalescence of the British and Fennoscandian ice sheets at that time, which could have directly influenced sea-surface environments in the vicinity of core MD99-2281.

Absence of internal tidal beams due to non-uniform stratification

A linear internal-tide generation model is applied to the Faeroe–Shetland Channel, using observed profiles of stratification. Several degrees of simplification are considered: 1) uniform, i.e. constant N; 2) vertically varying N (z); 3) the full N(x, z) and associated geostrophic background flows. It is shown that clearly identifiable internal tidal beams and internal-wave attractors occur in the first case, but not in the other cases where the pattern is patchy due to internal reflections from the strong inhomogeneities in the medium. Given the general occurrence of pycnoclines and geostrophic background flows in the ocean, it is argued that this internal scattering can be expected to be a widespread phenomenon.

Mapping hydrate stability zones offshore Scotland

Abstract One practical method to reduce environmentally damaging greenhouse gas emissions is through the geological storage of carbon dioxide. Deep, warm storage of carbon dioxide is currently taking place at Sleipner, North Sea and Weyburn, Canada. It is, however, also possible to store carbon dioxide as a liquid and hydrate in cool, sub-seabed sediments. Offshore north and west of Scotland seafloor pressures and temperatures are suitable for hydrate formation. In addition to the possibility of natural methane hydrate being present in this region, conditions may also be favourable for carbon dioxide storage as a liquid and hydrate. A computer program has been developed to calculate the depth to the base of the carbon dioxide and methane hydrate stability zones in two offshore regions: the Faeroe–Shetland Channel and the northern Rockall Trough. Results predict that methane hydrate remains stable to a maximum depth of 650 m below the seabed in the Faeroe–Shetland Channel, and 600 m below the seabed in the northern Rockall Trough; the carbon dioxide hydrate stability zone extends below the seabed to a depth of 345 and 280 m, respectively. No physical evidence for the existence of natural hydrate in these regions has been confirmed. Suitable conditions for carbon dioxide storage as a liquid and hydrate exist, and should this storage method be developed further, a more refined program and greater offshore investigations to improve data sets would be necessary to scope the full potential.

Marine downscaling of a future climate scenario for the North Sea

The SRES A1B scenario for the period 2072–2097 with the Bergen Climate Model (BCM) has been downscaled for the marine climate in the North Sea using the Regional Ocean Model System (ROMS). The results are compared to the 20C3M run for the period 1972–1997. The results show a warming of the North Sea, with a volume average of 1.4 °C, and a mean SST change of 1.7 °C. The warming is strongest in May–June. Geographically the strongest warming in the North Sea is found towards Skagerrak–Kattegat in the surface waters and in the central North Sea at 50 m depth. The downscaling show a weak increase in the Atlantic inflow to the North Sea. The BCM scenario has a change in the wind stress pattern in the Faeroe Island region. This strengthens the branch of Atlantic Water flowing west of the Faeroes and weakens the flux through the Faeroe–Shetland Channel. As a result both BCM and the downscaling show large changes in the temperature in this area, with weak warming and sometimes cooling south of the Faeroes and strong warming on the north side.

The geometry and emplacement of conical sandstone intrusions

Conical sandstone intrusions with a geometry comparable with that of many igneous sills have been identified using 3D seismic data from large areas of the North Sea and Faeroe–Shetland Basins. These intrusions are of reservoir scale, ranging from 100 to 2000 m or so in diameter, 50–300 m in height, and 1–80 m in thickness (aperture). They are concentrated in specific stratigraphic intervals in the Cenozoic fills of both basins. Two geometrical end members are recognised and defined here: ‘apical cones’ and ‘flat-based bowls’. The former consist of inward dipping conical inclined sheets meeting at a prominent apex and the latter of similarly dipping discordant margins climbing from the edges of a concordant sheet. Both end members are associated with domal folds that are interpreted as resulting from the hydraulic elevation of the overburden during intrusion, and which are analogous to similar structures associated with bowl-shaped igneous sills. Measurements of aperture ( ω) versus distance exhibit systematic relationships with the structural relief of these folds, offering a potentially predictive method for estimation of sandstone intrusion aperture and reservoir volume prior to drilling. A growth model for these end-member geometries is presented, drawing on existing theory for igneous sill emplacement. Aperture versus distance plots ( ω – X) are used to illustrate two contrasting models for aperture inflation during propagation, but these require much further data before any specific growth model can be adopted.

Marine downscaling of a future climate scenario for the North Sea

The SRES A1B scenario for the period 2072–2097 with the Bergen Climate Model (BCM) has been downscaled for the marine climate in the North Sea using the Regional Ocean Model System (ROMS). The results are compared to the 20C3M run for the period 1972–1997. The results show a warming of the North Sea, with a volume average of 1.4 °C, and a mean SST change of 1.7 °C. The warming is strongest in May–June. Geographically the strongest warming in the North Sea is found towards Skagerrak–Kattegat in the surface waters and in the central North Sea at 50 m depth. The downscaling show a weak increase in the Atlantic inflow to the North Sea. The BCM scenario has a change in the wind stress pattern in the Faeroe Island region. This strengthens the branch of Atlantic Water flowing west of the Faeroes and weakens the flux through the Faeroe–Shetland Channel. As a result both BCM and the downscaling show large changes in the temperature in this area, with weak warming and sometimes cooling south of the Faeroes and strong warming on the north side.

Marine downscaling of a future climate scenario for the North Sea

The SRES A1B scenario for the period 2072–2097 with the Bergen Climate Model (BCM) has been downscaled for the marine climate in the North Sea using the Regional Ocean Model System (ROMS). The results are compared to the 20C3M run for the period 1972–1997.The results show a warming of the North Sea, with a volume average of 1.4 ◦C, and a mean SST change of 1.7 ◦C. The warming is strongest in May—June. Geographically the strongest warming in the North Sea is found towards Skagerrak—Kattegat in the surface waters and in the central North Sea at 50 m depth. The downscaling show a weak increase in the Atlantic inflow to the North Sea.The BCM scenario has a change in the wind stress pattern in the Faeroe Island region. This strengthens the branch of Atlantic Water flowing west of the Faeroes and weakens the flux through the Faeroe—Shetland Channel. As a result both BCM and the downscaling show large changes in the temperature in this area, with weak warming and sometimes cooling south of the Faeroes and strong warming on the north side.

3D seismic analysis of the West Shetland Drift system: Implications for Late Neogene palaeoceanography of the NE Atlantic

Detailed seismic stratigraphic analysis of the West Shetland Drift, located on the Shetland Margin of the Faeroe–Shetland Channel, has been undertaken using commercial 3D seismic data. Emphasis was placed on the interpretation of a significant plastered contourite drift body, the West Shetland Drift–Slope section, with the aim of reconstructing the palaeoceanographic regime of the West Shetland slope during the past 5 Ma. Although limited in areal extent, the West Shetland Drift Slope section provides a key record of the depositional environment and bottom current activity on the West Shetland slope during the Late Neogene. The drift body was divided into three seismic–stratigraphic units and depositional processes responsible for each unit were interpreted, resulting in proposal of an evolutionary model in which a mixed downslope–alongslope depositional system was succeeded by alongslope current derived contourite drift deposition during the Early Pliocene to Mid-Pleistocene. During this time SW flowing alongslope currents impinged upon the West Shetland slope between the basin floor and a mid- to upper slope position. The final stage of deposition consisted of slope wedge progradation associated with Mid- to Late Pleistocene glaciation. Contourite deposition on the West Shetland Slope was punctuated by periods of glaciation activity, during which alongslope current activity appears to have been disrupted, suggesting a link between alongslope current activity and glaciation. Detailed mapping of key, smaller scale features, including a spectacular bottom current sediment wave field and iceberg ploughmarks, both of which were identified for the first time during this study, was instrumental in constraining the palaeocurrent regime, and would not have been possible without the high spatial resolution of the 3D seismic data. This study therefore highlights the efficacy of 3D seismic data as a tool for large scale spatial and temporal analysis of contourite drifts palaeoceanographic research.

Deep‐water mass source and dynamic associated with rapid climatic variations during the last glacial stage in the North Atlantic: A multiproxy investigation of the detrital fraction of deep‐sea sediments

In order to investigate North Atlantic Deep Water (NADW) dynamics and variability during the last glacial stage, a very high resolution multiproxy analysis of the detrital fraction of sediments deposited during Heinrich event 4 and Dansgaard‐Oeschger cycles 8 and 7 has been conducted on three deep‐sea cores. These cores are distributed along the path of the North Atlantic Deep Water from the Faeroe Shetland Channel to the Reykjanes ridge and the Irminger basin. The concentration in fine‐grained magnetites, the Ti‐content, and the smectite percentage within the clay minerals show similar and coeval fluctuations at each site and are comparable from one site to the other. This is the imprint of the detrital fraction originating from the northern basaltic provinces and transported to the studied sites. The average grain size in the fine fraction indicates a transport by deep‐sea currents. Therefore the observed fluctuations illustrate changes in the vigor of the bottom currents associated with the NADW with weak currents during cold periods (Heinrich 4 and stadials) and reactivation of the bottom circulation during interstadials.

The penultimate deglaciation: High-resolution paleoceanographic evidence from a north–south transect along the eastern Nordic Seas

The penultimate termination has been studied with focus on oceanographic changes in the eastern Nordic Seas and the influence of these changes on the surrounding ice sheets and vice versa. Repeatedly, major changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) occurred during the studied interval. Times of strong overturning and increased heat transport northwards were of importance in triggering one minor and two major disintegration events. The two major disintegration events were separated by a deglacial pause, characterized by a strong AMOC. The same variability is seen throughout the eastern Nordic Seas, from the Faeroe–Shetland Channel in the south to the Fram Strait in the north. Some of the oceanographic changes occurring during the penultimate termination are comparable with changes seen through the last deglaciation. Reduced winter moisture flux and increased summer melting due to the present insolation forcing further amplified the rate of ice sheet disintegration. Calculated sea-level change through TII shows a mean change of 121 ± 4 m, 41 ± 16 m in the first step and 80 ± 13 m in the last step.

Silicic acid enrichment in the deep water of the Faeroe–Shetland Channel

To evaluate the relative contribution of continental slope sediments, resuspended particles and settling material to the refuelling of dissolved silica in a high-energy environment, a study was conducted in the Faeroe–Shetland Channel (FSC), one of the main pathways of the newly formed Atlantic Deep Water. Fluxes of silicic acid (DSi) to the water column determined by multiplying the DSi concentration gradient by the vertical eddy diffusion coefficient showed a maximum at mid-slope (600–800 m) with values reaching up to 1700 μmol m−2 d−1 near the seabed. The mere dissolution of settling biogenic silica, estimated at 30–120 μmol m−2 d−1, cannot account for this refuelling of the deep-waters of the FSC with DSi. Benthic DSi effluxes on the slope, obtained both from incubations and from modeling pore water DSi profiles, indicated higher fluxes at mid-depth which corresponds to a zone of enhanced deposition and higher biogenic silica content. Contribution of DSi from benthic fluxes range from 370 to 740 μmol m−2 d−1 and can, to a large extent, sustain the enhanced calculated flux in the water column. Furthermore, the recurrent resuspension of bottom material, as observed at mid-slope being associated with turbulent flow, contributes to the increase in DSi concentrations in the deep water of the FSC with fluxes ranging from 60 to 800 μmol m−2 d−1. Our data illustrate the importance of the geomorphological setting of the basin which, with its shallow depth, funnel shape and turbulent conditions, favors the erosion and resuspension of surface sediment and the deposition of relatively fresh sediments at mid-slope, hence focusing the refuelling of passing waters with DSi.

Silicic acid enrichment in the deep water of the Faeroe–Shetland Channel

To evaluate the relative contribution of continental slope sediments, resuspended particles and settling material to the refuelling of dissolved silica in a high-energy environment, a study was conducted in the Faeroe–Shetland Channel (FSC), one of the main pathways of the newly formed Atlantic Deep Water. Fluxes of silicic acid (DSi) to the water column determined by multiplying the DSi concentration gradient by the vertical eddy diffusion coefficient showed a maximum at mid-slope (600–800m) with values reaching up to 1700μmolm−2d−1 near the seabed. The mere dissolution of settling biogenic silica, estimated at 30–120μmolm−2d−1, cannot account for this refuelling of the deep-waters of the FSC with DSi. Benthic DSi effluxes on the slope, obtained both from incubations and from modeling pore water DSi profiles, indicated higher fluxes at mid-depth which corresponds to a zone of enhanced deposition and higher biogenic silica content. Contribution of DSi from benthic fluxes range from 370 to 740μmolm−2d−1 and can, to a large extent, sustain the enhanced calculated flux in the water column. Furthermore, the recurrent resuspension of bottom material, as observed at mid-slope being associated with turbulent flow, contributes to the increase in DSi concentrations in the deep water of the FSC with fluxes ranging from 60 to 800μmolm−2d−1. Our data illustrate the importance of the geomorphological setting of the basin which, with its shallow depth, funnel shape and turbulent conditions, favors the erosion and resuspension of surface sediment and the deposition of relatively fresh sediments at mid-slope, hence focusing the refuelling of passing waters with DSi.

Post-breakup compression of a passive margin and its impact on hydrocarbon prospectivity: An example from the Tertiary of the Faeroe Shetland Basin, United Kingdom

Post-breakup compression of a passive margin and its impact on hydrocarbon prospectivity: An example from the Tertiary of the Faeroe Shetland Basin, United Kingdom

Ekman-induced turbulence over the continental slope in the Faeroe–Shetland Channel as inferred from spikes in current meter observations

Data from Aanderaa RCM-8 current meters, deployed on the continental slope of the Faeroe–Shetland Channel between depths of 471 and 1000 m, show intermittent spike-like reductions in current speed of ∼20–40%. The spikes have a duration of only one data value, corresponding to the unusually short sampling period of 1 min. Associated with the spikes are concurrent deflections in the current direction records, with a mean value of 7° and in a predominantly clockwise sense. The spikes furthermore occur only when the current direction has a poleward long-slope component when the shallow water is to the right. We reject instrumental deficiency as the cause of the spikes, and find that the negative bias is caused by the cosine response of the mechanical current meter when misaligned with the mean flow. The misalignment is due to turbulence generated by instabilities in the bottom boundary layer (BBL) caused by the downslope Ekman transport of buoyancy. The veering in current direction between 8 and 47 m above the seabed and the hourly averaged current direction are consistent with such a mechanism, whilst the intermittency is explained by the bursting phenomenon in a BBL. Both the quasi-period of ∼600 s and the duration of the spikes are in accordance with previous fieldwork and laboratory experiments and, in conjunction with a thickening of the boundary layer induced by the downwelling Ekman transport, explain the predominance of the spikes at heights of 34 and 47 m. Oblique internal wave reflection also plays a potential role in generating turbulence at the upper interface of the BBL higher up the slope where the stratification is comparatively strong, but the Ekman transport represents the dominant mechanism. Our findings cause concern for the reliability of data from traditional rotor- and vane-type current meters sampling at lower rates in turbulent near-bed regions where the turbulent properties of the flow will be averaged out in the sampling process, potentially causing an underreading of the true current speed.

Intense mid-slope resuspension of particulate matter in the Faeroe–Shetland Channel: short-term deployment of near-bottom sediment traps

An array of four moorings was deployed on a transect perpendicular to the south-eastern slope of the Faeroe–Shetland Channel to measure near-bottom fluxes during a 12-day period in spring 1999. Each mooring combined current meters and two sediment traps equipped with optical backscatter sensors (OBS) situated at 2 and 30 m above the bottom, at water depths of 470, 700, 800 and 1000 m. During the deployment, near-bottom current velocities at 470, 700 and 800 m water depth increased abruptly to values as high as 55 cm s −1 (within a few hours). The sudden change in the cross-slope component of the current at 470 m was immediately followed by a severe drop in temperature at this depth, and large fluxes were intercepted in the mid-slope traps (700 and 800 m) on the same day, probably associated with the strengthening of the along-slope component. Organic carbon and nitrogen content of the trap samples were, except for the shallowest mooring, much lower than in particulate matter suspended in the water column. During the high flux event, particles possessed lower organic carbon and nitrogen values than during lower flux periods. This indicates that sedimentary material entered the traps. A simple multi-component mixing model was applied to the trap samples to estimate the relative contribution to our total mass fluxes of material from different sources: primary settling from the water surface, rebound material, and the relatively aged sediment. It showed that fluff was the main contributor to the resuspended flux but that sediment proper was resuspended at mid-slope during the strong increase in the current velocities and represented up to 70% of the total mass flux at that time. This study shows that near-bottom resuspension on the slope may be intense and, although the scale is here short-term the phenomena described might be larger in time and space.

Integrated wide‐angle and near‐vertical subbasalt study using large‐aperture seismic data from the Faeroe—Shetland region

Acquiring large‐aperture seismic data (38 km maximum offset) along a profile crossing the Faeroe—Shetland basin in the North Atlantic enables us to use wide‐angle reflections and refractions, in addition to conventional streamer data (0–6 km), for subbasalt imaging. The wide‐angle results are complemented and confirmed by images obtained from the conventional near‐vertical‐offset range. Traveltime tomography applied to the wide‐angle data shows a low‐velocity layer (3.5–4.5 km/s) underneath southeastward‐thinning lava flows, suggesting a 2.5–3.0‐km‐thick sedimentary layer. The velocity model obtained from traveltime tomography is used to migrate wide‐angle reflections from large offsets that arrive ahead of the water‐wave cone. The migrated image shows base‐basalt and sub—basalt reflections that are locally coincident with the tomographic boundaries. Application of a new multiple suppression technique and controlled stacking of the conventional streamer data produces seismic sections consistent with the wide‐angle results. Prestack depth migration of the near‐vertical offsets shows a continuous base‐basalt reflection and a clearly defined termination of the basalt flows.

A Detailed Comparison of a Range of Three-Dimensional Models of theM2Tide in the Faeroe–Shetland Channel and Northern North Sea

Abstract A three-dimensional hydrodynamic model of the Faeroe–Shetland Channel and northern North Sea is used to investigate the spatial variability of M2 tidal elevations and currents in the region. This area is chosen because it covers a range of water depths. Also, there is a significant database of tidal elevations (namely 41 gauges) and current meters (namely 89 observations) with which comparisons can be made. With the exception of a couple of measurements made at the shelf edge, which may be influenced by the internal tide, namely a 180° phase shift across the thermocline due to a first mode internal tide, the observations correspond to those of a barotropic tide. Two different approaches are used to represent the profile of tidal currents in the vertical. In the first a spectral/functional method is used, while in the second a finite difference grid is applied. A range of parameterizations of vertical eddy viscosity (suitable for deep water regions) are used, from ones in which viscosity is relate...